This invention relates to a blood pump system including a blood pump control system for driving a roller blood pump of the type used in hemodialysis systems.
Prior art blood pump systems used in hemodialysis systems have a number of operating disadvantages which it is the purpose of the present invention to overcome. One of the most important features of a blood pump system used in hemodialysis is precise regulation of the speed of the motor driving the blood pump. This is important because the precise regulation of blood flow can be critical for the patient from a physiological standpoint. Prior art systems do not provide as precise a regulation as desired. Along with this flow rate regulation it is necessary for the system's operator to know the exact flow rate. Systems currently available do not provide a direct digital readout of flow rate but merely provide an analog relative scale which the operator must correlate to blood flow rate. In order to protect against motor overload prior art systems use electromechanical circuit breakers to disable the motor. Such circuit breakers are relatively slow operating and are not particularly precise in terms of the level at which switching occurs. Another problem with many prior systems is that they use 110 volt motors which operate directly off line voltage. Such systems have a relatively high leakage current which creates a much greater shock hazard potential for the patient. Also many prior art systems do not utilize an optimal design configuration which allows for use of a much smaller motor by reducing the peak torque required for driving the pump. U.S. Pat. No. 3,787,148 is an example of a prior art blood pump which does not utilize the optimal design. This reference shows a pump having an arcuate bearing surface defining an arc of 177.degree. and having lead ramps which diverge from the ends of the arcuate bearing surface by 10.degree.. Such configuration does not allow for the optimal peak torque reduction for rotation of the rollers. In addition the 10.degree. lead ramp divergence creates a somewhat abrupt change in the cross-sectional bore of the flexible tube through which the blood is pumped as the rollers approach and recede from the point of occlusion of the tube. Such change is also not desirable from the physiological viewpoint of the patient. Also prior art systems do not allow for a variable rate of independent adjustability of each of the rollers used in the roller pump or adjustment mechanism for adjusting the rollers which is located radially with respect to the main axis of rotation of the rotator head assembly.
The blood pump system of the present invention has the following features and advantages. Precise motor speed regulation is provided so that the blood flow rate of the blood pump can be accurately and precisely controlled for each individual patient. Another significant safety feature from the patients' viewpoint is that leakage current is greatly reduced thereby significantly lowering the potential shock hazard to the patient. The system also incorporates electronic circuit breakers which are much faster and precise in their level of switching. Motor overload and runaway protection circuitry is provided as further safety protection for the patient. By using a low voltage D.C. motor coupled with an isolation transformer as opposed to a 110 volt line operated motor, the efficiency of the system is maximized, as well as permitting a great reduction in the size and weight of the components used, especially with respect to the power transformer, the filter capacitor, the heatsinking required and the size of the motor used. A digital readout of the blood flow rate is provided so the operator need not make any extrapolations or correlations but has a direct digital readout. This feature also increases the safety of the system from the patients' viewpoint. The size of the components is also reduced by optimizing the peak torque reduction and optimizing the graduation of change in cross-section of the bore of the flexible tube used through which the blood is pumped by choosing the optimal design configuration for the arcuate bearing surface and lead ramps used in the roller pump used in the system.